Welding timer



July 15, 1941. H. ADLER 2,248,929

' WELDING TIMER.

Filed Dec. 14, 19:58

lAAllA 7 6'95 or vapor filled 22 Pea #07 0 F a/rafting WITNESSES:INVENTOR f2. C I Hans f7d/er:

ATTORNE Patented July 15, 1941 'WELDING TIMER Hans Adler,Berlin-Haseihorst, Germany, assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application December 14, 1938, Serial No. 245,650 InGermany March 5, 1938 19 Claims.

The invention relates to a short time circuit breaker through which aload is connected for a predetermined number of alternating currentperiods to an alternating current network. As circuit interrupter, gasor vapor filled paths, preferably grid controlled mercury vapordischarge paths with are type discharge, serve. The invention consistsof a novel construction of the control circuit determining the ignitionof the discharge paths; the circuit differs from the known short timeswitches advantageously by the fact that the operating requirements puton such a circuit breaker may he fulfilled with simple and inexpensiveswitching means. One of the essential characteristics of the inventionconsists in the fact that in the control circuit determining theignition time-point of the discharge paths, two potentials differingfrom each other are effective. One of the potentials has a peaked waveform; accordingly rises steeply and remains positive only during acomparatively short time. This potential determines the ignitiontime-point when the discharge path is first connectedin. The secondpotential which is effective in the same control circuit has, incontrast to the first potential, an essentially wider wave form.Accordingly, it maintains its positive value during a relatively longtime. This potential is only brought into action after the ignition ofthe dis-'- charge paths is initiated by the first potential of peakedwave form, and if the discharge paths are to remain conducting during anumber of half waves of the feeding alternating current potential.

The manner of. operation of a short time circuit breaker functioning inthis manner with different control potentials will be explained more indetail with reference to the exemplary embodiment shown in the figure.

A welding transformer l, the secondary winding of which is connected towelding electrodes 2, is connected through two grid controlled dischargevessels 3 and i with mercury cathodes to an alternating current network.In the grid circuit of the discharge vessel 3, there are a blockingpotential source 5 and an impedance 6 which may be connected in acircuit through a grid controlled arc discharge vessel 1, preferably ahot cathode discharge vessel. The potential for the circuit of theimpedance 6 is supplied by a transformer 8 which is connected to thesame alternating current source as the welding transformer. Theimpedance 6 and the auxiliary discharge vessel 1 are so connected thaton the ig nition of the discharge vessel 1, a potential differenceexists across the impedance 6 which counter-acts the blocking potential5 in the grid circuit of the discharge vessel 3 and thereby ignites thevessel.

The second discharge vessel 4 which is connected in the primary circuitof the welding circuit in antiparallel to the discharge vessel 3 isignited by a transformer 9, the primary winding ill of which isconnected to the primary terminals of the welding transformer I. Thetransformer 9, accordingly, obtains potential as soon as the weldingtransformer is connected through the discharge vessel 3 to thealternating current source. A secondary Winding 92 of the transformer 9is connected in the grid circuit of the discharge vessel 4 and ignitesthe latter discharge vessel after the current during the previous halfcycle of the feeding alternating current potential is extinguished inthe previously ignited discharge vessel 3. By the two discharge vessels3 and 4, at least two successive half waves of the feeding alternatingcurrent potential are thus supplied by means of the transformer I at anytime.

A measure for the time during which the Welding transformer I remainsconnected through the two discharge vessels 3 and 4 is the controlcircuit of the auxiliary discharge vessel 1. In this control circuit,there act, in accordance with the invention, in addition to a negativeblocking potential l0, two alternating potentials which are supplied tothe two impedances (resistances) H and I2 connected between the grid andthe cathode of the discharge vessel 1. The potential diiference acrossimpedance H is supplied by a transformer [3, the primary winding ofwhich is connected to the transformer 8 and thereby to the feedingalternating source. The transformer [3 produces across the impedance II,a potential difference of peaked wave form, 1. e., a potential whichbecomes positive only during a comparatively short time compared to thehalf wave of the feeding alternating potential. For converting thesinusoidal potential into a potential of peaked wave form, means areused which, in .the technical art of controllable discharge vessels,are, in general, known. It is essential that the potential supplied bythe transformer I3 shall have such a phase position that when thewelding transformer l is first connected in, the passage ofnon-permissible high current impulse through the main discharge vessel 3shall as far as possible be precluded. In accordance with the inductanceof the welding transformer or any other load connected through the shorttime circuit breaker to the feeding network, the ignition potential ofthe transformer [3 must lag the feeding alternating current potential bya smaller or greater phase angle which, for welding transformers ofsubstantial power, amounts to approximately 60-70 electrical degrees,for example.

The second control potential in the grid circuit of the discharge vessel1, which is supplied to the impedance E2, is also an alternatingpotential. It is not derived from the feeding network directly butthrough a secondary winding 43 of the transformer 3. The potentialdifference across impedance it may thus first appear after the firsthalf wave of the alternating current potential has been connected inthrough the main discharge vessel 3. In contrast to the potentialdifference across the impedance H, the potential difference acrossimpedance I2 has a wide curve shape. It accordingly, remains, positiveduring a substantially longer time. It may, for example, be sinusoidalor rectangular shape. A further characteristic which is essential forthe potential difference across impedance [2 consists in the fact thatthis potential shall lead the potential difference across impedance H inphase. It is preferably at least so far displaced ahead that it is inphase with the feeding alternating potential. It is, preferable,however, to provide additional means to cause the potential differenceacross impedance E2 to lead the alternating current potential. In theexemplary embodiment, a capacitor, i is provided for this purpose. Inlieu of this capacitor, other known means, for example, bridge circuitsor the like, may naturally be used for the purpose of attaining thedesired phase lead.

The two control potentials for the auxiliary discharge vessel 1impressed on the impedances H and i2, are so dimensioned that thepotential difference across impedance l2 determines the ignitiontime-point of the discharge vessel 1 as soon as both potentials aresimultaneously effective. The potential difference across impedance l2alone, accordingly, determines the ignition time-point after thedischarge vessel 3 becomes conductive by the operation of the potentialof peaked wave form impressed on the impedance ii at the beginning ofthe total on time of the short time circuit breaker. The potentialdifference across impedance l2 has the same eifect as is attained in thepresent short time circuit breakers by causing a practically invariabledirect current potential to act in the grid circuit of the maindischarge paths after the discharge paths are first rendered conductive.The advantage of the invention as compared to these known circuitsconsists in the fact that special auxiliary potentials are not necessarybut that all control potentials may be derived from the feedingalternating current source. The phase lead of the control potentialacting on the impedance i2 provided in accordance with the inventionassures that the discharge vessel 3 will, with certainty, receive apositive grid potential at the instant at which the current in theparallel connected discharge vessel 4 becomes extinguished, Thistime-point is not fixed but depends on the effective inductance of thewelding transformer which, as is known, may fluctuate in accordance withthe magnitude of the charge in the arms of the welding machine.

In addition to the negative blocking potential source it] and the twoimpedances H and I2, there is, in the circuit of the discharge vessel 1,a condenser E5. The latter supplies, in itself, in

til

known manner, a potential which, measured from the time-point of theconnecting in, gradually rises, and after the passage of a predeterminednumber of half waves, removes the ignition effect of the potentialdifference across impedance 12. The condenser i5 is, for this purpose,charged through a rectifier l6 and a regulating impedance H from thesecondary winding 94 of the transformer 9. Because of the derivation ofthis potential from the transformer 9, the charging starts only as soonas the welding transformer is connected in through the discharge vessels3 and 4. The condenser It may be short circuited by a switch l8 so thatit may be discharged to t prepare for a new operation.

At the terminals of condenser l5, there is connected, in accordance withthe invention, still another potential which is derived through arectifier l9 from the transformer 20, The transformer 20 is connected tothe secondary winding of transformer 3 and thereby to the feedingalternating current potential source. Through the transformer 20, thecondenser i5 is thus permanently charged, nevertheless, in contrast tothe above described charging circuit, with such a small charging currentthat only the characteristic losses of the condenser I5 are equalized.In the charging circuit of the transformer 20, an impedance 2| isconnected for limiting the charging current and it is considerablylarger than the regulating impedance H which measures the charging fromthe transformer 9. The additional charging from the transformer 20should prevent he blocking potential of condenser is from disappearingafter the end of a time switching process, if, for any reason, theswitch [8 short circuiting the condenser 15 is not closed; accordingly,if, for example, the operator of the welding machine permits the footswitch of the welding machine to remain actuated for a substantial timeand thereby holds the welding electrodes on the workpiece although thewelding process has already been terminated.

t has already been mentioned that potential difference across impedance12 in the grid circuit of the auxiliary discharge vessel 1 should be sodimensioned that this potential alone determines the ignition time-pointeven if the potential difference of peaked wave form is at the same timeeffective across impedance II. If the potential difference acrossimpedance 1! leads, by a sufficient angle, the potential difference ofpeaked wave form on impedance I l, the potential peak of impedance lllies behind the maximum of a sinusoial alternating current potentialeffective on impedance l2. The potential peak does not act (even afterthe potential difference across condenser [5 has become sufficient toprevent ignition of valve 1 by the potential difference across impedancel2) if it is so dimensioned that it does not jut out over the maximumvalue of the potential difference across impedance l2. A further meansof attaining the same result consists in introducing means in the gridcircuit of the discharge vessel 1, which provide that all the potentialseffective in this circuit together do not exceed a predetermined maximumvalue. For this purpose, a discharge path 22 may be connected inparallel to the two impedances H and [2, as is indicated in the figure.The total potential difference across the impedances and thus the totalpotential measuring the ignition of the discharge vessel 1, may then,even if both potentials are simultaneously effective, not exceed apredetermined value. Regardless of the relative phase position of thetwo alternating potentials on the impedances II and I2, the dischargevessel 1 and with it also the discharge vessel 3, is always ignited atthe instant at which the potential difference of wide wave shape acrossimpedance l2 exceeds the blocking limit of discharge vessel 1. In lieuof the glow discharge path 22, other potential limiting means may beused, such as, for example, a grid leak resistance which may be sodimensioned that the potential drop manifested on it for large gridpotentials prevents a further rise in the potential. Also by it, theupper part of the total potential acting on the grid may be cut oil.

A switching process of the time switch illustrated in the figure anddescribed in detail above develops as follows: When the weldingelectrodes on the welding machine are engaged with the work-piece, theswitch 18 in the grid circuit of the auxiliary discharge vessel 1 isopened by a foot switch or by a similar switching apparatus, undercertain circumstances, with an auxiliary relay interposed. One of thetwo contacts of this switch lifts a short circuit path parallel to thetwo impedances ii and I2 so that the potential differences across onthese impedances become cfiective and the discharge vessel 1 may ignite.In addition, the short circuit on the condenser i is also opened by theswitch I 8. As soon after the opening of the switch [8 as the positivepotential peak is manifested for the first time on impedance Ii, thevessel 1 ignites, supplies the impedance 5 and thereby at the sameinstant ignites the discharge vessel 3 in the primary circuit of weldingtransformer l. Thereby the transformer 9 obtains potential which, on theone hand, through its secondary winding 92 ignites the discharge vessel4 in the following half wave and, on the other hand, through a secondarywinding 93 supplies leading potential to the impedance ill in the gridcircuit of the discharge vessel T. This potential renders the peakedpotential difference across impedance H ineffective and supplies theignition of the discharge vessel 1 in the succeeding half wave. Thiscontinues until the condenser is charged up through 3e secondary winding94 of transformer 9 to a point such that its potential counteracts thepotential difference across impedance iii. The discharge vessel 7 thenis not ignited in the succeeding half wave. correspondingly, theignition potential difference across impedance 6 disappears and the twodischarge vessels 3 and 4 also extinguish. If the foot or control switch!8 is closed after this time switching process, the condenser i5 maydischarge. In addition the two impedances H and I 2 are short circuited.The next switchini process may take place in the above-described manneronly if the contacts of the switch 18 are opened. If, for any reason,the switch 18 is maintained open for a substantial time, the dischargevessel l is, in spite of this, not ignited because the discharge takingplace through the characteristic losses of condenser I5 are equalized bythe permanent charging from the transformer 20.

I claim as my invention:

1. Time switching apparatus for spot welding machines, comprising twogas, or vapor, discharge valves connected in anti-parallel between aload and an alternating current source, said discharge valves having acontrol circuit, means for impressing a plurality of potentials in saidcontrol circuit, said means including means for impressing a firstpotential of peaked wave form pressing a to initiate the ignition ofsaid discharge valves, and means for impressing a second potential ofwider wave form effective to maintain said discharge valves conductingonly after the ignition of the discharge valves.

2. Time switching apparatus according to claim 1, characterized by thefact that the first and second potentials are de ived from thealternating current source.

3. Time switching apparatus for spot welding machines, comprising twogas, or vapor, dis charge valves connected in anti parallel between aload and an alternating current source, control circuit means for saiddischarge valves, means for impressing in said control circuit means aplurality of potentials derived from the alternating current source,said means for impressing potential including means for impressing afirst potential of peaked wave form to initiate the ignition of saiddischarge valves, and means for impressing a second potential of widerwave form effective to render said discharge valves conduct ing onlyafter the ignition or the discharge valves, said means for impressing asecond poten tial including a transformer which is eifective only afterthe first ignition of the discharge valves.

4. Time switching apparatus for spot welding machines, comprising twogas, or vapor, discharge valves connected in anti parallel between aload and an alternating current source, control circuit means for saiddischarge valves, means for impressing in said control circuit means a 1of potentials derived from the alternat- -nt source, said means forimpressing potential including means for impressing a first potential ofpeaked wave form dephased relative to the potential of the alternatingcurrent source to initiate the ignition of said discharge devices, andmeans for impressing a second potential of wider wave form in phasewith, or leading, the potential of the alternating source and effectiveto reinitiate the ignition of said discharge valves only after theignition of the discharge devices by means of said 'irst potential, saidmeans for imseccnd potential including a transformer.

5. Time switching according to claim 4, characterized by the fact thatthe potential of peaked wave form is so dimensioned that it does not eX-ceed the maximum value of the potential or wide wave form onsimultaneous application of both potentials.

6. Time switching apparatus for spot welding machines, comprising twogas, or vapor discharge valves connected in anti-parallel between a loadand alternating current source, control circuit means for said dischargevalves, means for impressing a plurality of potentials in said controlcircuit means, said means for impressing potential including means forimpressing a first potential of peaked wave form to initiate theignition of said discharge Valves and means for inn pressing a secondpotential of wider wave form effective to render said discharge valvesconducting only after the ignition of the discharge valves by means ofsaid first potential, and said control circuit means including potentiallimiting means comprising a closed discharge path which does not permitthe total potential resulting from the first and second controlpotentials to exceed a predetermined value.

7. Time switching apparatus for spot Welding machines, comprising twogas, or vapor, main discharge valves connected in anti-parallel betweena load and an alternating current source, control circuit means for saidmain discharge valves, said circuit control means comprising anauxiliary discharge device having a grid circuit, two impedances and acapacitor connected in series in said grid circuit, means for impressinga plurality of potentials in said grid circuit, said means forimpressing potential including means for impressing a potential ofpeaked wave form across one of said two impedances to initiate theignition of said main discharge valves and means for impressing apotential of wider wave form across the other of said impedance, saidlast named potential being effective only after the ignition of the maindischarge valves, means for gradually charging said capacitor after theinitiation of the ignition of the main discharge valves, and a controldevice adapted to shunt the two impedances and also the capacitor atwill.

8. Time switching apparatus according to claim 7, characterized by thefact that a glow discharge path is connected in parallel to the said twoimpedances in the grid circuit of the auxiliary discharge device.

9. Time switching apparatus according to claim '7, characterized by thefact that an auxiliary potential is impressed across said capacitorthrough a high ohmic resistance to compensate for the losses of saidcapacitor.

10. For use in controlling the supply of power from a source to a loadthe combination comprising in efiect a first electric discharge valveand a second electric discharge valve interposed between said source andsaid load, means for arbitrarily rendering said first valve conductive,means for thereafter rendering said second valve and said first valveconductive in succession in response to current flow respectivelythrough said first valve and said second valve and means, in-

cluding means responsive to current fiow through said valves, forrestraining said valves from becoming conductive after they have beenrendered conductive a predetermined number of times.

11. For use in controlling the supply of power from a source to a loadthe combination commeans for thereafter rendering said second valve andsaid first valve conductive in succession in response to current flowrespectively through said first valve and said second valve, means forrestraining said valves from becoming conductive after they have beenrendered conductive a predetermined number of times and additional meansfor preventing said means for arbitrarily rendering said first valveconductive from functioning after said restraining means has functionedif said arbitrary means is maintained in the condition for renderingsaid first valve conductive.

12. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve connectedin anti-parallel between said source and said load, means for supplyinga potential to render said first valve conductive, means for thereafterderiving potentials from said load as it is supplied through said firstand second valves to render said second and first valves respectivelyconductive in succession and means for deriving a further potential fromsaid load as it is supplied through said first and second valves forrestraining said valves from being rendered conductive after apredetermined number of half periods of said source.

13. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve conheatedin anti-parallel between said source and said load, means for supplyinga first potential to render said first valve conductive, means forthereafter deriving second and third potentials from said load as it issupplied through said first and second valves respectively to rendersaid second and first valves respectively conductive in succession, saidthird potential being superimposed on said first potential and saidfirst potential having an amplitude no greater than said thirdpotential, and means for deriving a fiuther potential from said load asit is supplied through said first and second valves for restraining saidvalves from being rendered conductive after a predetermined number ofhalf periods of said source.

14. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve connectedin anti-parallel between said source and said load, means for supplyinga first potential to render said first valve conductive, means forthereafter deriving second and third potentials from said load as it issupplied through said first and second valves respectively to rendersaid second and first valves respectively conductive in succession saidthird potential being superimposed on said first potential and means forderiving a further potential from said load as it is supplied throughsaid first and second valves and superimposing it on said first andthird potentials for restraining said valves from being renderedconductive after a predetermined number of half periods of said sourceand means for limiting the magnitude of the sum of said first and thirdpotentials to a value less than said further potential.

15. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve connectedin anti-parallel between said source and said load, means for deriving afirst periodic potential from said source to render said first valveconductive and means for thereafter deriving second and third periodicpotentials from said load as it is supplied through said first andsecond valves respectively to render said second and first valvesrespectively conductive in succession, said third potential beingsuperimposed on said first potential and leading it in phase.

16. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve connectedin anti-parallel between said source and said load, means for deriving afirst periodic potential of short duration compared to a half period ofsaid source from said source to render said first valve conductive at apredetermined instant in a half period of said source, and means forthereafter deriving second and third periodic potentials from said loadas it is supplied through said first and second valves respectively torender said second and first valves respectively conductive insuccession said third potential being superimposed on said firstpotential and leading it in phase.

1'7. Apparatus according to claim 12 characterized by the fact that thefurther potential is derived by charging a capacitor through aregulating resistor.

18. Apparatus according to claim 13 characterized by the fact that thevalves are controlled through an auxiliary valve in the control circuitof Which certain of the potentials for rendering the valves conductiveand non-conductive are impressed.

19. For use in controlling the supply of power from a source ofalternating current to a load the combination comprising a firstelectric discharge valve and a second electric discharge valve connectedin anti-parallel between said source and said load, means for supplyinga first potential to render said first valve conductive, means forthereafter deriving second and third potentials from said load as it issupplied through said first and second valves respectively to rendersaid second and first valves respectively conductive in succession, saidthird potential being superimposed on said first potential and means forderiving a further potential from said load as it is supplied throughsaid first and second valves and superimposing it on said first andthird potentials for restraining said valves from being renderedconductive after a predetermined number of half periods of said sourceand means for limiting the magnitude of the sum of said first and thirdpotentials to a predetermined value.

HANS ABLE-R.

